The song is catchy on its own, but when Justin Bieber and Selena Gomez tweeted about it in 2012 it immediately took off and by summer, became unavoidable. But YouTube users still seek it out: It's been watched more than 455 million times in its 14-plus months on YouTube.

Most-watched YouTube videos of all-time

10:26 AM May 14, 2013

Though silly pet videos might be the first thing that comes to mind when most people think of YouTube, the most-viewed uploads since the service launched in 2005 don't feature a single pet. In fact, of the estimated 72 hours worth of video uploaded every minute to YouTube, the most-viewed content is almost entirely music videos. But don't equate it with MTV just yet: one of the top all-time videos is not musical. Click through the gallery to find out which one.